Cilia and flagella are complex microtubular organelles that are ubiquitous among eukaryotes, including humans, where they are found in the respiratory tract, the female reproductive tract and on sperm cells. Ciliary and flagellar dysfunction resulting from the absence of dynein arms has been reported to cause respiratory and fertility problems in humans and other mammals. Movement of cilia and flagella is driven by a complex group of molecular motors, the axonemal dyneins. The long-term objectives of this work are to understand how all the different dyneins are organized in ciliary axonemes and to understand the role(s) of each different dynein in ciliary motility. We will attempt to answer those questions by using targeted gene knockout techniques to introduce mutations into six genes encoding the 1-headed inner arm dynein heavy chains in the unicellular protozoan, Tetrahymena thermophila. The specific aims of this project are: I Complete targeted gene knockouts of six different Tetrahymena inner arm dynein heavy chain genes; II Determine which dynein heavy chain is encoded by each of the six mutated inner arm dynein heavy chain genes; III Assign each inner arm dynein to a specific location in the axoneme; IV Test the multi-dynein hypothesis by determining the effect(s) of the different KO mutations on cell motility and feeding. The results of this work should add to our understanding of dynein organization and function in cilia and flagella.